Magnetostrictive resonator mounting



P 1959 F. LEONARD ETAL 2,906,972

MAGNETOSTRICTIVE RESONATOR uoum'mc Filed May 3, 1956 INVENTORS FREDERICK LEONARD FLOYD B. CRAIG United States Patent 2,906,972 MAGNETOSTRICTIVE RESONATOR MOUNTING Frederick Leonard, Forest Hills, and Floyd B. Craig, Pitcairn, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 3, 1956, Serial No. 582,612 s 1 Claim. (Cl. 333 71) This invention relates to mountings for electro-mechanically resonant circuit elements, and more particularly to a mounting and assembly which imposes a minimum of motional impedance or mechanical restraint upon the vibratory elements.

For purposes of clearly illustrating the present inven tion, it will be described with specific reference to a magnetostrictive resonator of ring-shaped or annular type which has recently acquired recognition as a sharply resonant circuit element which can be advantageously employed in place of piezoelectric units in the lower range of the frequency spectrum, particularly for frequencies ranging downward from about one megacycle per second.

Magnetostrictive resonators until recently have been of little practical importance, for the older type require the use of auxiliary magnetic biasing structure or circuitry, and employ materials which are characterized by storage or quality factors Q of comparatively low value. Presently using cores composed of ferrite (sometimes referred to as a ferro-spinel) which exhibit high permeability in the order of hundreds, and provided in toroidal or other annular configurations having the inherent and desirable characteristic of retaining near-optimum magnitudes of residual magnetism after having been suitably excited, magnetostrictive resonators such as that later described exhibit Q factors of the order of several thousand and, because of the closed magnetic loop structure and residual magnetism characteristic, avoid the need for any com plicating auxiliary biasing circuitry or structure. One of the practical difficulties heretofore encountered in connection with magnetostrictive resonators of the type above-mentioned, however, is that conventional mounting structures therefor have not been entirely satisfactory from the standpoint of imposing minimum motional impedance to the vibratory action in order to realize substantially the maximum value of the Q factor, nor have they been fully satisfactory even from the standpoint of mechanical stability. For example, a commonly employed type of mounting involves supporting the ringshaped or annular magnetostrictive core by means of wires soldered or otherwise supposedly bonded to the sides of the core, but such a core supporting technique often proves unreliable. The supporting wires often break loose, probably because of vibration fatigue induced at their junctions by vibration of the supporting wires. Further, such supporting technique makes replacement or substitution of cores a troublesome matter.

It is therefore a primary object of the present invention to provide an improved magnetostrictive resonator assembly.

It is another object of this invention to provide a magnetostrictive resonator assembly which imposes minimum restraint upon the vibratory magnetostrictive core.

Another object of this invention is to provide a magnetostrictive resonator assembly in which the core is in effect floated with respect to its associated winding.

A further object of the invention is to provide a magne- 2,906,972 Patented Sept. 29, 1959 tostrictive resonator mounting which is easily assembled and adjusted.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. 1 is an exploded view of the novel magnetostrictive resonator structure;

Fig. 2 is a view in perspective of the assembled magnetostrictive resonator structure; and

Fig. 3 is a cross-section of the assembled structure taken on the line 3-3 of Fig. 2.

Referring to Figs. 1 and 3 for the most detailed showing of the novel structure, the magnetostrictive core 10 is formed as an annulus of say a simple nickel-ferrite material (74.69 grams of NiO to 159.68 grams of 'Fe O processed by heating to a temperature in the range 1300 to 1400" centigrade for about one and one-half hours, then cooled slowly). The necessary biasing magnetization of the annular ferrite core 10 in a closed flux loop without free poles may be provided in any desired manner, several techniques being available for this purpose, but details thereof otherwise being of no essentiality to the present invention. The driving magnetic field which must be superposed upon the constant bias flux in the annular core is in this instance arranged to be circumferential and thus colinear with the bias flux to result in extension or contraction of the ferrite material along circular elements of the annular core during magnetostrictive action thereof, and to thus preferably provide what is termed a radial mode of operation. To accomplish such a radial mode of operation, in some instances a single conductor passing through the central aperture of the annular core may be provided to serve as the winding, but the illustrated embodiment includes a multi-turn winding 12 as a preferable arrangement which simplifies the design of any utilization circuit (not shown) with which this magnetostrictive resonator may be employed. The winding is omitted in the cross-sectional view given in Fig. 3, in order to permit better illustration of the remaining structure.

The assembly herein disclosed is arranged to mount annular core 10 by light clamping between a lower group of supportingelements, preferably three in number, which may be supplied as pointed wire pins 14, and a like upper group of wire pins 16 (hidden from view in Fig. 1, but shown in Fig. 3), extending from screws 18 and 20, respectively, and secured thereto as by soldering or other fastening technique. The group of screws 18 (head ends not visible in Fig. 1, but see Fig. 3) which carry the lowermost wire pins '14 are threadedly secured to a circular end plate 22 of the assembly, and symmetrically positioned thereon along a circle which is intermediate between the inner and outer diameters of annular core 10. The group of screws 20 which carry the uppermost wire pins 16 are positioned and threadedly secured to an adjustable pressure plate 24 in like manner, with the wire pins extending from the lower face of the pressure plate toward annular core 10. The upper face of pressure plate 24 is provided with a centrally positioned cavity 26 to pivotally accommodate the rounded end of a pressure screw 28 which extends through upper plate 30 as shown. Suitable adjustment of pressure screw 28 will thus serve to maintain annular core 10 in clamped position between lower end plate 22 and pressure plate 24 without flexing the wire pins 14 and 16, and with equalized pin pressure as insured by the universally pivotal action inherent to the described pressure screw and pressure plate arrangement.

The pins 14 and 16 may be formed of Phosphor bronze wire, or other such material characterized by low energy absorption when exposed to vibratory motion during magnetostrictive action of annular core it). They are preferably provided in a length which is substantially one-fourth (or odd multiple; thereof) of the wave length in the wire material at the operating frequency, and further may be terminated in a low-energy absorption material at their base junctions with screws 18 and 20 to provide essentially complete energy reflection therefrom. In addition to supporting the annular core by means of 'wire pins 14 and 16 in such manner as to impose minimum restraint upon the vibratory action, the multi-turn driving coil 12 wound about core 10 is supported out of contact therewith by means of concentric inner and outer coil-support members 32 and 34 to further avoid deteriorating the 'Q factor. Lower end plate 22 is provided with a centrally-positioned post 36 upon which may be threadediy secured the cylindrical inner coil-support member 32, the latter having an outer diameter less than the inner diameter of the annular ferrite core 10, say by onesixteenth inch which is enough for core centering and clearance purposes. Outer coil support member 34 is annular in configuration, fixedly secured between the end plates 22 and 30 and in spaced relationship thereto by means of spacers '38 and 40 and clamping studs 42, and suitably dimensioned to provide like clearance from the centered core. The coil-support members are somewhat thicker than annular core 10, say by one-thirty-second inch, so that the coil turns will not bear against the upper and lower faces of the core. Post 36 is shouldered, as indicated, at a height such that the upper and lower faces of the inner coil-support member 32 will extend beyond the upper and lower faces of the annular ferrite core 10 by substantially equal amounts, and spacers 38 are made of suitable length to position outer coil support member 34 in like manner.

Annular or toroidal magnetostrictive resonators of the type here described require no more than several coil turns in their driving winding, and the inner and outer coil-support members 32 and 34 are correspondingly provided with a sufficient number of suitably spaced wireclearance holes 44 and 46 through which the necessary coil turns may. be wound, as shown. These wire-clearance holes may be bored quite close to the coil-support member surfaces which face the annular core, in order to reduce the effective diameter of the coil turns to minimum value. Additional wire clearance holes (notshown) may be provided to accommodate possible increase of coil turns where the assembly is intended for experimental purposes.

The circular end plates 22 and 3t and the outer coil support member 34 are assembled and fastened together in axial alignment by means of preferably three sets of the spacers 38 and 4t and clamping studs 42 as illustrated in Figs. 1, 2 and 3. Three clearance holes, or slots as shown, are correspondingly provided in pressure plate 24 so that it may have sufiicient freedom without interference by the adjacent spacers 40 to be positioned with its wire 4 pins 16 in light and uniform clamping engagement against the annular ferrite core 10. The adjustment of pressure screw 28 for such engagement may be rendered stable by any desired means, for example by provision of a friction washer 48 retained in an accommodating counter bore in end plate 30 as illustrated.

It will now be understood that the disclosed mounting technique provides practical means for achieving stable support of a vibrational member of a resonator device in a manner which realizes substantially floating action of the vibrationalmember in its operating environment, with negligibly small attenuation of the available Q factor of the resonator device even when the supporting elements are not positioned at nodal points or along nodal lines. It should also'be recognized that many modifications and variations can be devised Without departing from the inventive concept. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

'What is claimed is:

A resonator assembly, comprising: a ring-shaped magnetostrictive core member adapted to vibrate in a radial mode and having a pair of axially-spaced faces lightly clamped between first and second groups of resilient wire'pin elements, said resilient wire pin elements being of uniform length substantially equal to an odd multiple of one-fourth wavelength at the operating frequency of said core member; a supporting structure including a first end plate member to which the resilient wire pin elements of said first group are secured; a pressure plate member to which the resilient wire pin elements of said second group are secured; said supporting structure further including a second end piate member in which is threadedly engaged and through which extends an adjustable pressure screw having an end thereof bearing against said pressure plate at a central region therein relative to the group of resilient wire pin elements carried thereby, said end of the adjustable pressure screw being rounded to produce equalization of clamping pressure exerted by said resilient wire pin elements; and a' multiturn coil physically linkingsaid core member but with its turns out of contact therewith, said coil being supported by, and having its turns wound through apertures formed in, a pair of coil support members mounted upon said supporting structure and positioned inwardly and out- Wardly of said ring-shaped core member.

References Cited in the file of this patent UNITED STATES PATENTS 2,166,359 Lakatos July 18, 1939 2,435,487 Adler Feb. 3, 1948 2,504,719 Neilson Apr. 18, 1950 2,592,721 Mott Apr. 15, 1952 2,736,824 Roberts Feb. 24, 1956 2,762,985 George Sept. 11, 1956 

